U.S. Secretary of State Mike Pompeo announced Wednesday he has certified Saudi Arabia and the United Arab Emirates are working to prevent civilian casualties in their bombing campaign in Yemen.

Pompeo said he notified Congress on Tuesday of the determination, which allows for continued U.S. military aid.

"The Trump Administration has been clear that ending the conflict in Yemen is a national security priority," he said in a statement.

"We will continue to work closely with the Saudi-led coalition to ensure Saudi Arabia and the UAE maintain support for UN-led efforts to end the civil war in Yemen, allow unimpeded access for the delivery of commercial and humanitarian support through as many avenues as possible, and undertake actions that mitigate the impact of the conflict on civilians and civilian infrastructure," he added.

Impoverished Yemen has remained wracked by conflict since 2014, when Shia Houthi rebels overran much of the country, including the capital of Sanaa.

The conflict escalated the following year when Saudi Arabia and its Sunni-Arab allies launched a wide-ranging air campaign aimed at rolling back Houthi gains in Yemen.

The Saudi-led air campaign has been dogged by rights concerns, which were renewed Aug. 9 when a devastating airstrike on a school bus killed 40 children aged 6 - 11. Eleven other people were killed.

That was the latest in a series of attacks that stirred international outrage.

Representative Ro Khanna, a fierce opponent of U.S. military aid to Riyadh's coalition, called Pompeo's certification a "farce" shortly after it was made public.

"The Saudis deliberately bombed a bus full of children. There is only one moral answer, and that is to end our support for their intervention in Yemen. If this executive will not do it, then Congress must pass a War Powers Resolution," he said.

But U.S. defense chief James Mattis concurred with Pomeo, saying Riyadh and Abu Dhabi "are making every effort to reduce the risk of civilian casualties and collateral damage to civilian infrastructure."